I want to make a communication between citect and my plc using modbus ascii protocol via computer rs232 port. I want to make a communication cable for this. what I want to know is the connection diagram to make this cable?

 

Many industrial protocols need special cables because the protocol uses electrical characteristics that unique to it (and often proprietary). Modbus however will run over ordinary RS-232, so there is no special cable required. You need to find the section in your manual which tells you which pins do what on the connector you want to use. Often the manual will tell you how to make a cable. If not, then tell us the definition for each pin and someone here will be able to answer your question. However, nobody can answer your question unless you can provide them with that information.

Your question really needs to be phrased as "how can I make an RS-232 cable to connect port 'x' on PLC model 'y' to a PC?"

 

DB9 to DB9 on the PLC? or DB9 to RJ45 on the PLC?

Need to know. Typically, for Modbus communications. 2-3 / 3-2 / 4-6 / 6-4 / 5 - 5 / and 7-8 loopback both ends. Because of the loopbacks, a "standard null modem cable does not work.